A Common Agency with Incomplete Information
证明，当代理人拥有成本私人信息时，寡头企业组建共同代理可能反而不利，因为独立代理能通过收入信息限制代理人信息租金，而共同代理则消除了这一优势。
* In the present article I demonstrate that forming a common agency by oligopolistic firms may not be to their advantage, if agents have access to private information about their costs. Bernheim and Whinston (1985, 1986) pointed out that a common agency allows the firms to sustain the collusive outcome by giving them a vehicle to internalize the externality generated by their pricing or output decisions. If agents have access to private information, the advantage pointed out by Bernheim and Whinston may be more than outweighed by the possible existence of an informational disadvantage. Specifically, if the unit costs of different potential agents are correlated, the firm may be more successful in extracting the informational rents of its agent if it contracts with an independent agent, and not with the same agent as its rival firm. When oligopolistic firms contract with independent agents, the revenues of one firm reveal implicit information about the unit costs of agents serving competing firms in the same industry. However, if the unit costs of different agents are correlated, revenues also reflect information about the unit cost of the firm's own agent. This additional information transmitted by revenues cannot be controlled by the agent's reporting behavior. As a result, if the firm conditions its agent's payoff upon revenues, it can limit the informational rents that this agent can secure due to the existence of private information. This possibility of limiting its agent's informational rents is eliminated if the firm contracts with the same agent as its rivals. With a common agency, the agent can manipulate the reports delivered to all the firms, thus reducing the options available to each of them. Various patterns of agency relationship exist in markets where oligopolistic producers